The mucosal immune system is important for both the primary transmission of HIV-1 infections and the pathogenesis of AIDS-related secondary infections. The rate of transmission of HIV-1 is low compared to other sexually transmitted diseases. Host mucosal immune factors may contribute to this low rate, however, the underlying mechanisms are unknown. Mucosal immunoglobulin (Ig) may provide one mechanism of protection in seronegative patients. A subset of Ig that express the VH3 family of heavy chain genes (the largest family which comprises about 50% of the expressed systemic Ig repertoire) are known to bind HIV-1 gp120 and may serve as protective Ig in the uninfected host. In addition, B cells expressing VH3-Ig are known to be depleted in the blood of HIV-1 infected patients. The loss of this major subset of B cells may contribute to the limited ability of these patients to control AIDS-related secondary infections. Few data are available on VH gene expression in the mucosal immune system of humans. The goal of this proposal is to characterize the VH repertoire of mucosal B cells, particularly VH3 gene family usage, in both seronegative and HIV-1 infected patients, and determine the fate of these B cells during the course of HIV-1 infection. A semi-quantitative polymerase chain reaction protocol in conjunction with in situ hybridization will be sued to determine the frequency of VH gene usage in mucosal B cells from gastrointestinal and salivary gland biopsies. This work will also have direct implications for the design of mucosal vaccines against HIV-1 and related secondary infections, since the efficacy of some vaccines may require the expression of particular VH genes and thus, would be compromised if those genes are not expressed in the mucosal immune system.